Concerns about Pets and Wildlife

It's important to use rodenticides responsibly to minimize the risk of unintended exposure to non-target animals. Seeking professional advice and following product instructions can help prevent incidents of poisoning.

Primary Poisoning

Direct consumption of bait by animals.

Secondary Poisoning (Relay Toxicosis)

Consuming poisoned prey.

Key Considerations

  • Rodents consuming single-dose anticoagulants may pose a prolonged risk as residues can persist in their liver tissue for many weeks.
  • Rodents poisoned with multiple-dose anticoagulants can be toxic to animals that consume them.
  • Strychnine and zinc phosphide have potential risks of secondary poisoning for pets that eat poisoned rodents.
  • Awareness of the breakdown rates of rodenticides is crucial to assess the timing of secondary poisoning risks with substances like zinc phosphide.

It's important for individuals using rodenticides to be aware of these secondary poisoning risks and to take precautions to minimize harm to non-target animals. Responsible use and adherence to guidelines can help mitigate the environmental impact of rodenticide use.

Anticoagulant Rodenticides

Anticoagulant rodenticides work by inhibiting the normal blood clotting process in rodents, leading to internal bleeding and ultimately causing death.

Resistance

Anticoagulant resistance among rodents has led to the development of more potent single-dose anticoagulants, such as brodifacoum, bromadiolone, and difethialone. These substances require only one day of feeding to deliver a toxic dose, making them more effective against rodents that have developed resistance to multiple-dose anticoagulants like warfarin, chlorophacinone, and diphacinone.

Signs of Toxicity

  • Uncontrolled bleeding (may not be obvious).
  • Difficulty breathing, weakness, lethargy.
  • Less common signs: coughing, vomiting, blackened stools, paleness, bleeding from gums, seizures, bruising.

Multi-Dose Anticoagulants

Secondary Poisoning Risk

Even multiple-dose anticoagulants may be poisonous to animals consuming poisoned rodents.

Warfarin

Year Registered: 1950

Discovery: Found in moldy sweet clover that made a herd of cattle sick.

Resistance: Became less effective over time as rodents developed resistance.

Feeding Requirement: Multiple doses over several days

Chlorophacinone

Toxicity: High secondary poisoning risks in mammals, dogs, and cats.

Feeding Requirement: Multiple doses over several days.

Diphacinone

Toxicity: High secondary poisoning risks in mammals, dogs, and cats.

Feeding Requirement: Multiple doses over several days.

Single-Dose Anticoagulants

Risk Scenario

If a rodent continues to feed on the single-dose anticoagulant after consuming a toxic dose on the first day.

Potential Risk

The rodent may accumulate more than a lethal dose in its body before clotting factors run out.

Residue Persistence

Residues of single-dose anticoagulants may remain in liver tissue for many weeks.

Risk for Predators

Predators consuming many poisoned rodents over time may build up a toxic dose.

Brodifacoum

Toxicity: More toxic than multiple-dose anticoagulants. High secondary poisoning risks in birds, mammals, dogs, and cats.

Feeding Requirement: Single-dose anticoagulant – one day's feeding can deliver a toxic dose.

Bromadiolone

Toxicity: More toxic than multiple-dose anticoagulants. High secondary poisoning risks in birds, mammals, dogs, and cats.

Feeding Requirement: Single-dose anticoagulant – one day's feeding can deliver a toxic dose.

Difethialone

Toxicity: More toxic than multiple-dose anticoagulants. High secondary poisoning risks in birds.

Feeding Requirement: Single-dose anticoagulant – one day's feeding can deliver a toxic dose.

Non-Anticoagulant Rodenticides

Multi-Dose Non-anticoagulants

Cholecalciferol

Registration Year: 1984

Mode of Action: Vitamin D3; disrupts calcium balance leading to various systemic effects.

Toxicity: Requires rodents to consume several doses for toxicity.

Time Lag: Time lag between exposure and signs of toxicity.

Toxicity: Potential secondary risks are not fully measured.

Signs of Toxicity

  • Weakness, depression, loss of appetite.
  • Vomiting, increased thirst, frequent urination, dehydration, constipation.
  • Signs may develop within 12 to 36 hours after exposure.

Single-Dose Non-anticoagulants

Bromethalin

Registration Year: 1984

Mode of Action: Inhibits energy production in central nervous system cells.

Toxicity: Considered a single-dose rodenticide.

Breakdown Product: Major breakdown product is more toxic than bromethalin itself.

Toxicity: Potential secondary risks are not fully measured.

Signs of Toxicity

  • Muscle tremors, seizures, sensitivity to light or noise.
  • Hyperexcitability if a lethal dose is consumed.
  • Signs may develop 8 to 12 hours or several days after ingestion.

Zinc Phosphide

Registration Year: 1947

Mode of Action: Converts into phosphine gas in the presence of water and acid.

Toxicity: Phosphine gas blocks cellular energy production, affecting various organs.

Human Exposure: Breathing in zinc phosphide dust or phosphine gas can cause respiratory distress.

Secondary Poisoning Risk

May cause secondary poisoning in pets.

Conditions for Risk

Secondary poisoning risk exists when the stomach of the rodent still contains intact pellets of zinc phosphide.

Breakdown Rate

Zinc phosphide breaks down quickly, so the rodent must be very recently dead or just dying for secondary poisoning to pose a risk.

Signs of Toxicity

  • Vomiting (may smell like garlic), anxiety, weakness, difficulty breathing, convulsions.
  • Signs may be delayed for 4 hours or longer.
  • Phosphine gas exposure is damaging to the heart, brain, kidney, and liver.

Strychnine

Registration Year: 1947

Source: Derived from seeds of certain plants (Strychnos nux-vomica and Strychnos ignatii).

Mode of Action: Affects spinal cord cells, causing nerve cells to fire more readily, leading to muscle spasms.

Use Restrictions: Products with more than 0.5% strychnine are restricted and sold only to certified applicators.

Secondary Poisoning

Pets that eat rodents poisoned with strychnine may experience secondary poisoning.

Signs of Toxicity

  • Involuntary muscle spasms, extreme extension of limbs.
  • Signs begin within 15 minutes in people and within two hours in animals.
  • Death is caused by impaired breathing.